Sea to Summit Spark SpI Down Sleeping Bag

5°C Comfort Limit (EN13537:2012), 180g of 850+ Fill Power ULTRA-DRY Down (US Method)
Weighs 342g (Regular bag)
Code: SS19446V
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UOG TOP PICK - Sea to Summit Spark Series Sleeping Bags - Best Warmth to Weight ratio - We've singled out Sea to Summits Spark sleeping bags as one of our recommendations because its a minimalist in the true sense of the word, it only includes a few key features but delivers exceptional warmth given its very low weight.

Sea to Summit says:

Ultra-light and technical, our Spark Series bags are designed to keep you as warm as possible while minimising packed weight and size.

The Spark Series spans everything from an ultralight liner to an expedition weight mid-winter bag. While the end usage is very different, they reflect a design ethos of matching weather conditions to the lightest bag possible.

The secret to the impressive performance is a combination of premium materials and careful design. The RDS 850+ Loft premium goose down, light-gauge #3 YKK zip and high performance 10D Nylon shell and 7D lining fabrics, set the stage for a superior performance. These materials are combined with a contoured mummy design for efficient insulation, and that mummy design is then tweaked for each model to best fit the use scenario.

Our Ultra-Dry Down water-repellent treatment protects the down from external moisture and condensation from the inside of the bag, virtually eliminating the negative effects moisture has on down. All Sea to Summit Down Sleeping Bags use Responsible Down Standard (RDS) certified down. The Ultra-Dry Down protection also makes the Spark an impressive hard-alpine or adventure racing bag, where every gram is counted and down has never been a viable option.

Sea to Summit's Spark SpI Down Sleeping Bag is a true minimalist bag that uses the lightest materials and highest quality, responsibly sourced  down to deliver an exceptionally high warmth to weight ratio, when compared to other similarly rated bags.

The Spark I bag features vertical baffles on the chest area to minimise movement of down, optimising insulation where you need it most. The half zip saves weight and reduces heat loss at the expense of venting if conditions are too warm. 

The contoured mummy shape isn't too constrictive and the super thin and light outer fabrics means more care will be needed than with more heavy duty bags. The bag compresses down to a very small size.

- Reviewed by Ultralight Outdoor Gear

Read reviews here:

UOG TOP PICK - Sea to Summit Spark Series Sleeping Bags - Best Warmth to Weight ratio - We've singled out Sea to Summits Spark sleeping bags as one of our recommendations because its a minimalist in the true sense of the word, it only includes a few key features but delivers exceptional warmth given its very low weight.

Help and advice: Choosing a sleeping bag advice
  EN 13537 rating for sleeping bags explained
  Sleeping bag shape and sizes advice
  Sleeping Bag features Page 1
  All about down filling in sleeping bags
  • Ultralight 7D and 10D fabrics for minimal weight and packed size
  • RDS 850+ Loft Premium Goose ULTRA-DRY Down for maximum insulation value
  • Contoured mummy shape for comfort and efficient insulation
  • Vertical chest baffles prevent down migration and cold spots
  • This bag is not designed to pair with another
  • Sewn through quilted construction minimises weight
  • Sewn through vertical baffles on chest optimises position of down to prevent it moving during use
  • 1/2 zip with single slider aids access while keeping weight to a minimum
  • Updated sizing provides extra room for both shoulders and hips while still maintaining insulation efficiency

Temperature Rating

  • EN13537:2012 Comfort: 9°C / 48°F
  • EN13537:2012 Comfort Limit: 5°C / 41°F
  • EN13537:2012 Extreme: -9°C / 15°F
  • Performance: Warm Weather

Regular Specs

  • Weight: 342g (excludes storage bags)
  • Fill weight: 180g
  • Fits up to: 6 ft / 183 cm
  • Internal Width Shoulder: 150cm / 59 in
  • Internal Width Waist: 130cm / 51 in
  • Internal Width Feet: 88cm / 35 in

Large Specs

  • Weight: 392g (excludes storage bags)
  • Fill weight: 205g
  • Fits up to: 6 ft 4 in / 192 cm
  • Internal Width Shoulder: 158cm / 62 in
  • Internal Width Waist: 138cm / 54 in
  • Internal Width Feet: 94cm / 38 in


  • Insulation: RDS 850+ Loft Premium Goose ULTRA-DRY Down
  • Shell: Ultralight 10D Nylon Shell
  • Zipper: Left-side #3 YKK zipper
  • Comes with: Ultra-Sil™ compression bag and storage cell
Showing our 1 review for Sea to Summit Spark SpI Down Sleeping Bag. Write a review ›
Review Summary - 5 out of 5 based on 1 rating.
September 9, 2019 | Rockin Rob
Wow, so small and so light but still works if you use it sensibly

Wasn't sure if this purchase would turn out to be a mistake and a step too far - trying to save weight from a Lightwave sleeping bag that already weighed just 600g. But, I tried it last night and with clear skies it dipped to 4C and all was good. I started the night with my normal thermal trousers (actually winter running tights) and a really thin short sleeve base layer but added a thin gilet I have for cycling which weighs only 100g or so in expectation of cold weather. I was armed in the tent with a Sea to Summit Thermolite bag liner, just in case it got too cold, along with a variety of other layers and even a warmer bag if I needed. At 4am it dipped below 4C and I needed a pee, so had to get out of my nice cosy environment and leave the tent to walk to the toilet block - it was super cold outside! Before I went outside, I added a thin long sleeve base layer to my top so I wouldn't be too cold and to help me warm up when I got back. I kept that on for the rest of the night and was again nice and cozy when back in the bag. Didn't need any of my other backup kit but might have had it got much colder. I run quite warm so would say the 5C minimum is about right when in a tent as long as you dress sensibly. You can stretch it if you bring the right things which is great as you can save weight if you think it will be warm enough and if you get it a bit wrong you can cope by using other layers you probably already have anyway. Great piece of kit. Once the down has distributed after you take it out the bag, it actually fills it reasonably well. Would be even better if the vertical baffles on the top of the torso section were box stitched as this is its weakest point when the temps reach the limits. Very happy with this.

Ultralight Outdoor Gear Limited